The present invention relates to an optical scanning device, such as a bar code scanner.
A bar code scanner is a device for reading the bar code on the surface of a commodity as an identification symbol to identify it, by optically scanning the bar code.
In connection with such a bar code scanner, Jpn. Pat. Appln. KOKAI Publication 2-178888 has disclosed a lightweight, portable bar code scanner. FIG. 32 is a front view of a laser scanning head 110 used in the bar code scanner. FIG. 33 is a vertical sectional view taken along line I-I' of FIG. 32. FIG. 34 is a transverse sectional view taken along line XXXIV-XXXIV' of FIG. 33. Numeral 111 indicates the body section. In the figures, the emitted light from a laser diode (hereinafter, referred to as LD) 133 passes through a focusing lens 132 and strikes a scanning mirror 119b. As the scanning mirror 119b is rotated by a scanning motor 124, this causes the reflected light to scan. The reflected light passes through a window 114, hits the bar code (not shown) located outside the head, and scans it. The reflected light from the bar code passes through the window 114, taking the reverse route of the emitted light, and strikes a condenser mirror 119a, which gathers the rays of light on a photosensor 117, which then senses the light.
The conventional optical system is characterized by selectively sensing the reflected light and scattered light from the vicinity of the area on which the emitted light is actually projected by causing the scanning mirror 119b to force the emitted light to scan at the same time that the condenser mirror 119a scans the visual field of the photosensor 117. This configuration minimizes the effect of external light. The scanning mirror 119b and condenser mirror 119a are integrally formed and caused to scan by the scanning motor 124. (Hereinafter, they are referred to as an integral scanning and receiving mirror 119).
In the prior-art optical system, the LD 133, focusing lens 132, integral scanning and receiving mirror 119, and photosensor 117 are used as bar code scanner component parts. They have to be positioned and assembled, which makes it difficult to reduce costs. Because the incident angle of light to the integral scanning and receiving mirror 119 is small (close to vertical incidence), the LD 133 and photosensor 117 have to be separated a suitable distance away from the integral scanning and receiving mirror 119 so that they may not block the reflected light. This makes it difficult to make the scanner more compact.
Furthermore, the focusing lens 132 for determining the position of the focal point of the emitted light is designed to have the ability to read the bar code relatively away from (several tens of centimeters from) the bar code scanner. In addition, the gathering mirror 119a is designed to have a much larger area than that of the scanning mirror 119b according to the distance to the bar code. With such a configuration, the large moving part requires the scanning motor 124 to produce a greater driving force, which makes it difficult to make the bar code scanner more compact. Moreover, an attempt to combine the scanning mirror 119b composed of a plane mirror and the condenser mirror 119a of a concave mirror into an integral structure raises the problem of complicating the mirror manufacturing method.